Method and device for producing gear plates for a continuously variable gearbox

ABSTRACT

The invention relates to a method for producing gear plates ( 1 ) for a continuously variable gearbox wherein at least two gear plates ( 1 ) with the transmission surfaces ( 2 ) thereof are arranged in an opposite mauler. When the gearbox is in operation, said transmission surfaces come into contact in a non-positive mode with a power transmission element, on a device comprising at least one workpiece spindle ( 3 ) and a grinding disc ( 4 ) which is driven by a grinding spindle ( 5 ) in order to grind the transmission surface ( 2 ) of at least one gear plate ( 1 ). During the grinding of the transmission surface ( 2 ), a repeated relative oscillating movement is carried out radially in relation to the workpiece spindle ( 3 ), between the grinding disc ( 4 ) and the gear plate ( 1 ), in such a way that the grinding region of the grinding disc ( 4 ) is moved back and forth between an inner radius ( 2.1 ) and an outer radius ( 2.2 ) of the transmission surface ( 2 ). The gear plate ( 1 ) is rotated by means of the workpiece spindle ( 3 ) in such a way that the entire transmission surface ( 2 ) is ground.

The present invention relates to a method as well as to an apparatus for the manufacture of transmission plates for a continuously variable transmission, such as a belt-and-pulley drive. Such a continuously variable transmission, also called a CVT, has at least one pair of transmission plates each with a substantially conical or spherical, i.e., curved, transmission surface. A transmission surface is herein to be understood the surface, at which forces are transferred. The transmission surface can have a shape that is curved or straight, radially across the transmission plate. The transmission plates arranged in pairs are adjustable as to the space between them, and a force-transferring element, such as a chain of fine links, for example, can be deflected between them. By adjusting the space between the plates, a continuous adjustability is achieved. In this case, the force-transferring element migrates positively along the transmission surface of the confronting transmission plates. In the operation of the drive, the force-transferring element is thus shifted up and down and from the inside out and vice versa on the transmission surface between an inside diameter and an outside diameter.

The problem exists here that the transmission plates have to be pressed against the force-transferring element with force sufficient to keep them from slipping. Any slippage must be prevented effectively. On the other hand, it is desired that the contact force of the transmission plates be kept as low as possible so as to prevent unnecessarily high surface pressure during the transfer of force from the transmission plates to the force-transferring element. Nevertheless, there must be no slippage between the transmission plates and the force-transferring element.

In producing such transmission plates for continuously variable transmissions, there is the problem, furthermore, that the plates must have a high-strength transmission surface machined to the closest possible tolerances. The high strength of the plate is important to maximum life of the transmission. Irregularities and distortion of the transmission surface of such plates are to be avoided in order to assure the trouble-free and quiet operation of the transmission.

It is therefore the object of the present invention to offer a method and an apparatus for producing transmission plates for a continuously variable transmission, with which the force-transferring properties between the plates and a force-transferring element are improved, the service life is lengthened, and especially slippage of the force-transferring element is reliably prevented.

This objective is accomplished by a manufacturing process with features of claim 1 and by an apparatus with the features of claim 10. Advantageous embodiments and further developments of the invention are subject matter of the dependent claims.

For the inventive method of producing transmission plates, a radial, relative pendulum-like motion with respect to the workpiece spindle is performed between the grinding wheel and the transmission plate for grinding the conical or spherical transmission surface, so that the grinding area of the grinding wheel on the transmission surface migrates between an inside radius and an outside radius of the surface. In this way the grinding pattern of the drive surface can be varied selectively. Instead of the substantially circular grinding pattern common in circular grinding, a cross grind, for example, can be produced with the inventive method. Cross grinding refers here to a grinding pattern, in which the cuts somehow cross one another. In this manner, the surface roughness of the drive surface can be controlled, thereby creating optimum conditions for avoiding slippage by a force-transferring element in the operation of the transmission. The surface can be produced within the necessary close dimensional tolerances and has the necessary strength. Since the surface roughness of the transmission plates is plainly improved by the controlled creation of the surface roughness of the transmission plates and slippage is prevented to a great degree, the contact pressure of the transmission plates can be further reduced, which results in a reduction of the surface-to-surface pressure and thus also of friction in the transfer of force and hence an improvement in the efficiency of the transmission. A continuously variable transmission having transmission plates manufactured according to the invention ultimately also leads to a reduction in the fuel consumption of an internal combustion engine in comparison with the fuel consumption of conventionally made transmissions.

Cross grinding, produced in this manner, offers the advantages that the percentage of contact area on the surface of the transmission plates is higher, since a “cross grind” is obtained similar to that produced on honed surfaces.

In the case of angular plunge cut grinding a peripheral grind develops, which must be surfaced precisely in the geometrically negative form, so that any shape error in the surfacing is imaged on the workpiece. On account of the pendulum-like motion, errors of shape in the surfacing become “distorted,” so that they are no longer imaged on the workpiece. Furthermore, cross grinding offers advantages with regard to the transfer of force at the point of force transfer. The pendulum-like grinding additionally creates less thermal stress on the workpiece during grinding, since the workpiece has fully cooled again by the time that the grinding wheel engages the same point once again.

According to an advantageous embodiment of the invention, the rotational speed of the workpiece spindle is coordinated with the pendulum-like motion. Thus, a uniform grinding pattern can be produced on the transmission surface in all areas. In this manner, too, the surface roughness can be increased or reduced deliberately. According to an advantageous aspect of the invention in this regard, the speed of the workpiece spindle is varied according to the radial grinding position of the grinding wheel on the transmission surface. Thus a uniform grinding pattern can be produced on all areas of the transmission surface, for example by increasing or reducing the workpiece spindle speed, especially by achieving equal grinding conditions at all points of grinding contact, so as to produce the same surface roughness on all circumferential areas of the transmission plate. This prevents the force transfer element from operating at different slippage limits at different positions on the transmission plate.

In another advantageous embodiment of the invention, the rate of the pendulum-like motion is varied according to the radial position of the grinding wheel on the transmission surface. By decreasing the rate of the pendulum-like motion toward the outer circumference, it is possible to prevent the grind texture from varying according to a particular location on the circumference. The relative pendulum-like motion can be performed by a back-and-forth movement either of the grinding wheel or of the transmission plate.

In another advantageous embodiment of the invention, two workpiece spindles are provided, which are associated with each other such that a pendulum-like motion across the transmission surfaces can be performed by two transmission plates, so that a pair of transmission plates can be ground in a vise with only one grinding wheel. The two workpiece spindles are so adjusted in this case that the transmission surfaces of the two plates are arranged adjacent one another, while the conical or spherical transmission surfaces each lie in a single plane. The machining of two mounted transmission plates by the method of the invention thus permits the manufacturing time to be reduced. The cycle periods can be approximately cut in half. It is obvious in this case that the workpiece spindle speeds are coordinated with the lengthened swing. According to one aspect of the invention in this regard, the two workpiece spindles can be turned about a common pivot point so that the transmission surfaces can be produced with a spherical surface shape. The position of the pivot point is determined by the radius of the spherical shape.

According to claim 10, the inventive apparatus for producing transmission plates for a continuously variable transmission has at least one workpiece spindle and one grinding spindle, the grinding spindle and the transmission plates being arranged so that, during the grinding operation, a relative pendulum-like motion across the transmission surface, in a radial direction with respect to the workpiece spindle axis, can be performed between the grinding wheel and the workpiece spindle. In this way the grinding pattern on the transmission surface can be influenced with the apparatus. Due to the pendulum-like motion it is possible, instead of the otherwise customary uniformly radial grinding pattern, to produce any desired grinding pattern on the surface, e.g., a cross grind, a grinding pattern spiraling outward, or any other desired grinding pattern. Thus it is possible with the apparatus to manufacture transmission plates with a desired and predefined surface roughness. The relative pendulum-like motion can be achieved preferably either by a grinding wheel that can be shifted back and forth or by a transmission plate that can be shifted in the same manner.

In an advantageous embodiment of the invention, a grinding wheel spindle carriage is provided, which is adjustable angularly with respect to the workpiece spindle. The grinding wheel spindle carriage permits precise and rapid shifting back and forth of the grinding wheel across the transmission surface being ground. Due to angular adjustability with respect to the workpiece spindle different conical shapes of transmission plates can be manufactured.

In an additional advantageous embodiment of the invention, the apparatus has a control system, with which the relative pendulum-like motion can be deliberately controlled. Thus the pendulum-like motion can be deliberately varied so that a predefined surface roughness of the transmission surface of the transmission plates can be established. According to an aspect of the invention in this regard, the rotational speed of the workpiece spindle and the velocity of the pendulum-like motion are variable. Thus, a great variety of surface roughness can be created with the apparatus. The machining of the transmission surface can thus be optimized for a particular application, i.e., with respect to its slippage and frictional properties in the operation of the transmission.

In another advantageous embodiment of the invention, the workpiece spindle can rotate about a pivot point to produce a “spherical” shape of the transmission surface. The pivot point is determined in this case by the desired or required radius of curvature. The rotational movement then also serves at the same time for producing the relative pendulum-like motion.

According to another advantageous embodiment of the invention, the apparatus has two workpiece spindles, which are adjustable for alignment and their spacing apart. The apparatus thus permits the simultaneous grinding of two transmission plates simultaneously, as well as the execution of the pendulum-like motion of the invention during the grinding. The manufacturing time can in this way be reduced. Due to the adjustability of the workpiece spindles as to the space between them, transmission plates of different size can be produced with a deliberately controlled surface roughness. Also, the cone angle is adjustable in this way. According to an aspect of the invention in this regard, the two-workpiece spindles can turn about a common pivot point; this permits the production of spherical or various surfaces on the transmission surfaces.

In another advantageous embodiment of the invention, the apparatus is part of a CNC machining center. In this manner, the transmission plates can be further processed in a single set-up. Changeover between different operating steps preceding or following the grinding operation is thus unnecessary.

The invention will be described in detail hereinafter with reference to the appended drawing, wherein:

FIG. 1 shows a diagrammatic plan view of a first embodiment of the inventive grinding apparatus;

FIG. 2 shows a diagrammatic plan view of a second embodiment of the invention using two workpiece spindles;

FIG. 3 shows a diagrammatic plan view of an embodiment alternative to the one in FIG. 1 and

FIG. 4 shows a diagrammatic plan view of an embodiment alternative to the one in FIG. 2.

A plan view of an inventive grinding apparatus is shown simplified in FIG. 1. The workpiece 1 is a transmission plate with a conical surface 2, clamped in a workpiece spindle 3. The transmission plate 1 has a conical transmission surface 2, i.e., it slopes in only one direction. It is obvious, however, that the transmission plate 1 can also have a shape sloping in two directions. A grinding wheel 4 is provided on a grinding spindle 5 to grind the conical transmission surface 2 of the transmission plate 1. The grinding wheel 4 and the grinding spindle 5 are provided on a grinding spindle carriage 6 such that the grinding wheel 4 can perform a pendulum-like motion while grinding the surface 2. For this purpose, furthermore, a control system 7 is provided, by which the rotational speed of the workpiece spindle 3 as well as the pendulum-like motion of the grinding wheel 4 can be controlled. During the grinding of the transmission surface 2, the grinding wheel 4 swings back and forth between an outside radius 2.2 and an inside radius 2.1 such that its tracks on the surface 2 cross one another. Thus a cross grind can be produced on the surface 2. With the apparatus it is therefore possible to control the surface roughness of the transmission surface 2 of the transmission plate 1. Particularly, the rotational speed of the workpiece spindle 3, the speed and direction of the pendulum-like motion of the grinding wheel can be established through the control system 7. Other adjustment parameters are the same as in conventional grinding machines, such as for example the movement of the grinding wheel 4 toward the surface in the X-Y plane.

FIG. 2 shows diagrammatically a second embodiment of the grinding apparatus of the invention in which, unlike the embodiment previously described, two workpiece spindles 3 and 3′ are provided. In this way it is possible with the apparatus to grind two transmission plates 1 and 1′ in one set-up. For this purpose the two workpiece spindles 3, 3′ are aligned with one another according to the cone shape of the transmission surface 2, 2′ such that the surface lines of each half of the conical surface 2, 2′ are in a single plane. The grinding spindle 5 is arranged on a grinding spindle slide 6, which permits a pendulum-like motion from the inside radius 2.1 of the surface 2 of the one transmission plate 1 to the inside radius 2.1 of the other transmission plate 1′. In this way the time required for the grinding of the transmission surface of transmission plates can be reduced.

FIG. 3 presents schematically an alternative embodiment of the grinding apparatus from FIG. 1. Instead of a movable grinding spindle 6, here the pendulum-like motion during grinding the transmission surface 2 is performed by a workpiece spindle 10, which can swing back and forth. Thus a radius shape, i.e., spherical shape of the transmission surface 2 is developed, which has a targeted surface roughness due to the cross-grinding that is generated. The position of the pivot point 8 determines the radius of curvature of the spherical surface and is preferably adjustable.

In FIG. 4, as in FIG. 3, an alternative embodiment of the grinding machine from FIG. 2 is represented diagrammatically with two workpiece spindles. The two-workpiece spindles 10, 10′ can pivot around a common point 9 such that the pendulum-like motion can be performed through the workpiece spindles 10, 10′, while grinding wheel 4 approaches in direction Y. The pivot point 9 is adjustable, as is the swing angle α to adapt the apparatus to various shapes of transmission plates. 

1. (canceled)
 2. The method of claim 21, comprising executing said coordinating so that a cross-grind of a predetermined roughness is produced on the transmission surface.
 3. The method of claim 21 or 2, comprising coordinating rotational speed of the workpiece spindle with the pendulum-like motion.
 4. The method of claim 3, comprising varying the rotational speed of the workpiece spindle according to radial position of the grinding wheel on the transmission surface.
 5. The method of claim 21 or 2, comprising varying speed of the pendulum-like motion according to radial position of the grinding wheel on the transmission surface.
 6. The method of claim 21 or 2, wherein said imparting of pendulum-like motion comprises imparting pendulum-like motion to the transmission plate.
 7. The method of claim 21 or 2, wherein said imparting of pendulum-like motion comprises imparting pendulum-like motion to the grinding wheel.
 8. The method of claim 21 or 2, wherein the apparatus comprises a second workpiece spindle and the method comprises grinding a transmission surface of each of two transmission plates in one set-up the relative pendulum-like motion being imparted for the grinding of both transmission plates in said one set-up.
 9. The method of claim 8, wherein said imparting of pendulum-like motion comprises imparting pendulum-like motion to the workpiece spindles by turning the workpiece spindles about a common pivot point and thereby producing a spherical form of the transmission surfaces.
 10. The method of claim 8, wherein said imparting of pendulum-like motion comprises imparting pendulum-like motion to the grinding wheel and thereby producing a conical form of the transmission surfaces.
 11. Apparatus for manufacture of transmission plates for a continuously variable transmission, in which at least one pair of the transmission plates are in frictional contact at transmission surfaces thereof with a force transfer element during operation of the transmission, the apparatus comprising at least one workpiece spindle a grinding spindle, a grinding wheel rotationally drivable by the grinding spindle about an axis of symmetry of the grinding wheel for grinding the transmission surface of at least one of the transmission plates, and means for imparting relative pendulum-like motion, between the grinding wheel and the transmission plate.
 12. The apparatus of claim 11, is comprising means for imparting back-and-forth motion to the grinding wheel.
 13. The apparatus of claim 11, comprising means for imparting back-and-forth motion to the transmission plate.
 14. The apparatus of claim 12, comprising a carriage for the grinding spindle, a central axis of the grinding spindle being horizontally adjustable in its angle to a central axis of the workpiece spindle.
 15. The apparatus of claim 13, wherein the workpiece spindle is rotatable about a pivot point to produce a spherical exterior shape of the transmission surface.
 16. The apparatus of any one of claims 11 to 15, further comprising a control system for controlling the relative pendulum-like motion.
 17. The apparatus of claim 16, wherein the control system controls rotational speed of the workpiece spindle and speed of the pendulum-like motion.
 18. The apparatus of any one of claims 11 to 14, further comprising a second workpiece spindle each for accommodating a respective transmission plate; the workpiece spindles being adjustable with respect to one another in their alignment and in their spacing apart with reference to a swing angle α.
 19. The apparatus of claim 18, wherein, the workpiece spindles are rotatable about a common pivot point to produce a spherical shape of the transmission surfaces.
 20. A CNC machining center comprising the apparatus of any one of claims 11 to
 15. 21. Method for producing transmission plates for a continuously variable transmission in which at least one pair of transmission plates is arranged with transmission surfaces thereof opposite to one another and in frictional contact with a force-transferring element during the operation of the transmission, the method being executed on an apparatus having at least one workpiece spindle, a grinding wheel and a grinding spindle driving the grinding wheel in order to grind the transmission surface of at least one of the transmission plates, the method comprising, during the grinding of the transmission surface, imparting relative pendulum-like motion between the grinding wheel and the transmission plate so that an area of grinding migrates back and forth between an inside radius and an outside radius of the transmission surface while rotating the transmission plate by means of the workpiece spindle so that the entire transmission surface is ground, and coordinating movements of the grinding wheel and the transmission plate with one another, so that, a non-circular abrasion pattern is generated on the transmission surface whereby roughness of the transmission surface is adjusted to a predetermined extent. 